Ground sensitive control for electrical apparatus

ABSTRACT

In a material moisture sensitive control, and integrating switch, in circuit with a pair of moisture sensing electrodes in a fabric drying apparatus, is operable between conductive and nonconductive postures as a function of the dryness condition of the fabrics being dried. A transistor is operable for initiating termination of operation of the apparatus responsive to a high voltage developed across the integrating switch in the nonconductive condition. In a preferred embodiment, the integrating switch is in the form of an electrolytic cell in a series circuit and connected at one terminal to earth ground through which a circuit must be completed for operability of the apparatus.

United States Patent [191 Cotton July 16, 1974 [54] GROUND SENSITIVE CONTROL FOR 3,521,376 7/1970 Beller 34/45 ELECTRICAL APPARATUS 3,522,660 8/1970 Elders 34/45 [75] lnventor: Curran D. Cotton, Newton, Iowa [73] Assignee: The Maytag Company, Newton,

Iowa

[22] Filed: Nov. 2, 1973 [21] Appl. No.: 412,456

Related US. Application Data [63] Continuation-impart of Ser. No. 405,203, Oct. 10, 1973, which is a continuation of Ser. No. 123,046, March 10, 1971, and a continuation of Ser. No. 803,637, March 3, 1969.

[52] US. Cl 328/4, 307/308, 34/45 [51] Int. Cl. G06n 27/00 [58] Field of Search 307/308; 328/4; 34/45, 34/48; 317/9 [56] References Cited UNITED STATES PATENTS 3,497,964 3/1970 Elders 1. 34/45 Primary Examiner-Rudolph V, Rolinec Assistant ExaminerB. P. Davis Att0mey, Agent, 0r Firm-William G. Landwier; Richard L. Ward 57 ABSTRACT voltage developed across the integrating switch in the nonconductive condition. In a preferred embodiment, the integrating switch is in the form of an electrolytic cell in a series circuit and connected at one terminal to earth ground through which a circuit must be completed for operability of the apparatus.

14 Claims, 2 Drawing Figures u; 6M J i /70 MAAA AA in HTENTEU JUU SHEET 2 OF 2 'geZ V 1 GROUND SENSITIVE CONTROL FOR ELECTRICAL APPARATUS CROSS REFERENCE TO RELATED APPLICATIONS This application is a continuation-in-part of pending application Ser. No. 405,203 filed Oct. 10, 1973, which was a continuation of application Ser. No. 123,046 filed March 10, 1971 and in turn of Ser. No. 803,637 filed Mar. 3, 1969.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a control system for an electrical apparatus and more particularly to a control system sensitive to the grounding of the apparatus for effectively requiring an earth grounding of the apparatus lected dryness condition. The presence of this elec-- tronic circuitry has made possible the use of at least a portion of the circuitry for also sensing the presence of an earth grounding of the electrical apparatus chassis. One such system is shown in the application Ser. No. 405,203 filed Oct. 10, 1973 of which this application is a continuation in part. This previous application points out the need for sensing a ground and provides circuit means requiring an earth ground for proper operability of the apparatus and thus indicating to the operator the absence of an earth ground connection.

There ishowever a continuing need for improved control systems providing still further operational and control features in electrical apparatus.

SUMMARY OF THE INVENTION It is an object of the'instant invention to provide a control circuit for an electrical apparatus operable for sensing the presence of an earth grounding of the apparatus.

It is a further object of the instant invention to provide an improved control circuit sensitive to thepres: ence of an earth grounding of the apparatus for opera bility thereof.

It is a further object of the instant invention to provide a control circuit for an electrical apparatus in which a ground sensitive circuit precludes operation of the apparatus in the absence of an earth grounding of the apparatus chassis.

It is a still further object of the instant invention to provide an improved control circuit for an electrical apparatus having a ground sensitive circuit operable for preventing energization of the apparatus if the apparatus is not connected to an earth ground.

These objects are achieved in a control circuit for an electrical apparatus where the control circuit includes a series circuit portion that is effectively connected to one of the power conductors on one side but is effec- 2 tively electrically disconnected from the second power conductor on the other side and is instead connected to an earth ground path for connecting the other side of the series circuit to the second conductor only through an external earth ground path so that the presence of the circuit through the earth ground conductor becomes av prerequisite to operability of the apparatus.

Operation of the device and further objects and advantages thereof will become evident as the description proceeds and from an examination of the accompanying two pages of drawings.

DESCRIPTION OF THE DRAWINGS The drawings illustrate a preferred embodiment of the invention with similar numerals referring to similar parts throughout the several views, wherein:

FIG. 1 is a view of a fabric drying apparatus partially broken away and sectioned and incorporating the control system-0f the instantinvention; and

FIG. 2 is an electrical schematic diagram of a preferred circuit embodying the dryness sensing control of the instant invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. I there is shown the overall construction for a clothes dryer including a cabinet assembly comprising a sidewall wrapper 11 having generally vertical opposite side panels 13 and a rear panel 14. The sidewall wrapper 11 is supported on a base 15 which in turn is supported on a horizontal surface through a plurality of adjustable feet 16. The cabinet assembly further comprises a front panel 19 and top cover 20 supported on the sidewall wrapper 11. The

top cover 20 includes an upwardly extending housing 21 for accommodating selected controls for the dryer such as a push to start mechanism operated by button 22.

The front panel 19 defines a generally central access opening 23 and includes a door 24 hinged on the front panel 19 and operable between open and closed positions relative to the access opening 23. The door 24 includes an outer panel 25 substantially flush with the front panel 19 and an inner panel 26 having a portion that extends rearwardly into the access opening 23. A

seal 29 supported by the inner panel 26 extends endlessly around the rearwardly extending portion of the inner panel 26 for engagement with a recessed portion 30 of the front panel 19 to effectively provide an air seal at the access opening 23.

Disposed within the cabinet assembly is a pair of spaced apart generally vertical bulkheads 33 and 34. The rear bulkhead 34 is fixed to the sidewall wrapper .11 by a pair of brackets such as the bracket 35 that includes a front flange connected to the bulkhead 34 and a rear flange connected with the rear panel 14. The

front bulkhead is similarly connected to the front flanges of wrapper 11 with a pair of brackets.

A generally cylindrical peripheral sidewall 36 is disposed between' the stationary bulkheads 33 and 34. At the front and at the rear of the peripheral sidewall 36 there are inwardly turned flanges comprising relatively short end walls 39 and 40 juxtaposed the front and rear bulkheads 33 and 34 and cooperablewith the sidewall 36 to effectively define a fabric tumbler 41. A-plurality of baffle members 43 are fixed to the peripheral sidewall 36 and extend into the tumbling chamber for assisting in the movement of fabrics therewithin during rotation of the fabric tumbler 41.

The front and rear bulkheads 33 and 34 include radially outwardly disposed recess portions 44 and 45 extending axially toward the front and toward the rear, respectively, of the dryer l0. Seals 49 and 50 are fixed to the bulkheads 33 and 34 in the recesses 44 and 45 and are engageable with the tumbler end walls 39 and 40 to provide an air seal at the ends of the tumbler 41. The bulkheads 33 and 34 also include generally annular portions 51 and 53 inwardly disposed from the recesses 44 and 45 that effectively provide extensions of the end walls 39 and 40 of the fabric tumbler 41.

. The seal member 49, for example, disposed between the stationary bulkhead 33 and the rotatable tumbler 41 is shown as a U-shaped or channel-shaped felt member having a pair of generally outwardly extending legs 54and 55 connected by an intermediate arcuate portion.'The leg 54 is fixed, as with adhesive, to the stationary bulkhead 33 in the recess 44 so that the intermediate arcuate portion conforms generally to the corner radius 56 and effectively biases the other leg 55 into engagement with the front wall 39 of the tumbler 41. The felt may be coated on one side with anantifriction layer such as polytetrafluoroethylene to provide a smooth, more'durable, and lower friction running surface for engagement with the tumbler end wall 39.

The front bulkhead 33 defines an access 57 into the tumbling chamber that is substantially aligned with the access opening 23 in the front panel 19. The rear bulkhead 34 defines an opening 58 to receive a perforate panel 59 through which airflow is directed into the tumbling chamber .60 from a duct system as will be shown.-

The tumbler 41 is supported on a generally horizontal axis bya system includinga pair of rollers 61 supported on brackets 62 fixed to the rear bulkhead 34 and by a pair of slide bearings (not shown) supported by similar brackets fixed to the front bulkhead 33. The tumbler 41 could be supported entirely on rollers or entirely on slides as conditions permit.

The fabric tumbler 41 is rotated byIa belt 63 encompassing the periphery of the tumbler sidewall 36 and driven by a motor 64 mounted on thebase 15.

The airflow system for the clothes dryer 10 includes a heater assembly 66 supported adjacent the base 15 and into which air is drawn from the atmosphere for heating prior to movement into the fabric tumbling chamber 60. The heater assembly 66 accommodates an electric heating coil as will be considered in greater detail as related to the controlcircuitry of FIG. 2. The heater assembly 66 is connected to a generally upwardly extending rear air duct 68 which conducts heated air from the heater assembly 66 through the rear perforate panel 59 and into the tumbling chamber 60.

The air then flows from the chamber 60 through a filter assembly 69 into the front air duct 70. The filter assembly 69 includes a filter screen 73 supported within the airduct 70 for removing lint particles from the air flowing'out of the tumbling chamber 60 into the front air duct 70. V

The air is drawn from the front air duct 70 into a blower assembly 74 from which it is forced through a rearwardly extending lower air duct 75 to atmosphere. The blower 74 includes an impeller (not shown) that is driven by the motor 64 mounted adjacent to the blower 74 on the base 15. The general airflow pattern within the drying apparatus 10 is shown by the'broken and solid line arrows in FIG. 1. I 1

In order to measure the electrical conductivity or resistance of the fabrics within the chamber 60, as a measure of the condition of dryness of the fabrics, electrodes or conductors and 81 are mounted within the chamber 60. In a preferred embodiment, the electrodes are in the form of a pair of spaced-apart elongated conductor members mounted on an insulating member 82 and in turn fixed to a lower portion of bulkhead 33 to provide a pair of electrically insulated contacting surfaces engageable by the fabrics tumbling within the.

tumblingchamber. It will be realized that different forms of electrodes or conductors may be used although the type disclosed herein is a preferred construction.

The electrical circuitry connected to the electrodes willbe explained in greater detail in the discussion of FIG. 2 hereinbelow. It is noted, however, that the cabinet and other conductive portions of the apparatus are electrically connected to each other and are in turn connected to earth ground by conductor 87.

Referring now to FIG. 2, the control circuitry includes three conductors that are connectable with a conventional three-wire 240 volt, alternating current supply. For the explanation of the circuitry of FIG. 2, it will be assumedthat conductors and 101 are connected with the power lines and that the conductor 103 is connected to the earth-grounded neutral line. If used in a 120 voltapparatus, the second power conductor 101 would be eliminated and all of the circuit portions would effectively be connected between conductors 100 and 103.

' The energizing circuit for the appliance includes a door switch 104 connected to conductor 100 and also includes a manually actuatable momentary push-tostart switch mechanism operated by button 22 as shownin FIG. 1 and which includes a first single-pole single-throw momentary switch 105 and a second single-pole double-throw momentary switch 106to be described further-herein. The closing of the contacts in the push-to-start'switch 105 effects energization of a control'relay including a coil l07 and a pair of single pole single-throw switches 108 and 109. The relay switch 108 is in the heater circuit while the relay switch 109 serves as a holding switch during operation of the apparatus. The relay operation in the control of the machine will be described in greater detail herein.

The electric heating coil 102 is connected between the first and second power conductors 100 and 101 by a circuit portion including the relay switch 108, a high limit thermostat 112, a cycling thermostat 110, and a centrifugal switch 111 in the motor 64. The centrifugal switch 111 is normally open but is operable to the closed position upon energization of the motor 64.

The drive motor 64 is initially energized by a circuit cuit. After initial energization of the motor 64 and operation of the centrifugal switch 113 to the normally open contact 117 and release of the push-to-start switch 105, the circuit for energizing the motor 64 and maintaining energization thereof will be completed from the first power conductor 100 through the door switch 104, the relay holding switch 109 and a conductor 119 to the normally open contact 117 of the centrifugal switch 113.

A cool-down thermostat 120 is also provided in the circuit to the motor 64 and is operable to a closed position at a predetermined temperature within the tumbling chamber 60 of, for example, 135 F. After the dryer apparatus has operated for a period of time with heat the cool-down thermostat 120 will close and maintain the motor 64 energized until the temperature is reduced to 135 F.'This cool-down thermostat 120 therefore provides a fabric cool-down operation following a heat On drying operation.

The lower portion of the circuit diagram of FIG. 2 comprises primarily the moisture sensing and automatic termination circuit for the fabric drying apparatus. It is the general function of this sensing circuit to measure the moisture content of the tumbling fabrics during the drying operation and to initiate termination of operation at a particular fabric dryness condition. The circuit is operable for utilizing the resistance of momentary electrical paths completed through random samples of tumbling fabrics within the drying chamber. Generally speaking, these values of resistance are integrated and after a time delay period the control indicates the presence of fabrics having a generally predetermined or preselected condition of dryness. A predetermined electrical condition within the circuit initiates termination of operation through an output circuit portion.

An integrating switch provides the integration of the random momentary resistance values. An electrochecmical device, such as an electrolytic cell 125, is used as the integrating switch in the preferred embodiment of FIG. 2 and is operable as a timer or as an integrator. Operationally, the electrolytic cell 125 functions as a switch having a conductive posture in which the resistance through the electrolytic cell is relatively low and a nonconductive posture in which the resistance through the electrolytic cell is relatively high. The electrolytic cell 125 is operable as a bidirectional electron or current flow integrator as will become clear from the following explanation.

More specifically, the electrolytic cell 125 is a reversible micro-coulometer device designed in accordance with F aradays law of electroplating. The device operates by means of the physical transfer of atoms of metallic silver across an electrolyte. The device has a central gold electrode, as shown schematically and designated by numeral 126 in FIG. 2 and a silver electrode shown as numeral 127, which also serves as the outer case. When current flows in one direction, namely, from the silver electrode 127 to the gold electrode 126, the positive silver ions in the electrolyte are deposited on the gold electrode 126. The effective resistance of electrolytic cell 125 and the corresponding voltage drop across the cell are low. When current is applied in the opposite direction, namely, from gold electrode 126 to the silver electrode 127, the silver is deplated from the gold electrode 126 but the device still exhibits a low resistance as long as there is silver remaining on the working or gold electrode 126. As soon as the silver has been depleted from this gold electrode 126, the electrolytic device 125 changes to a nonconductive or high resistance state, usually of the order of several megohms, with a corresponding voltage rise to over 800 millivolts.

In this specification, the convention that electrons flow by the same path as current and in the opposite direction thereto will be used. Therefore, electron flow through the electrolytic cell 125 from the gold electrode 126 to the silver electrode 127 will effect a plating of the gold electrode 126.

Since the flow of current through the electrolytic cell 125 is accompanied by a transfer of silver from one electrod to the other in a direct proportionality to the level and time of current flow, including periodic or random inputs of any time-current integral, the device is a true integrator of the current input over a time period. At any instant, the quantity of silver on the working or gold electrode 126 represents a true value of the integral of the current that has passed through the electrolytic cell 125 during the integrating function.

As a simple timing device the electrolytic cell 125 may be given an initial charge comprising a predetermined plating current flow, or current flow from the silver electrode 127 to the gold electrode 126, for a specific time to set or charge the device to a given level of plating. The electrolytic cell 125 may then be used to provide a time delay by connecting the electrolytic cell 125 to a circuit effecting an opposite current flow through the device for a deplating of the silver from the gold electrode 126.

A combination of both timing and integration is utilizedin the circuit of FIG. 2'as will be shown by the following detailed explanation of the circuit and operation thereof.

To set the electrolytic cell 125 for a guaranteed minimum timing function, a preplating circuit portion is connected between the first and second power lines and 101 for effecting a plating current flow through the electrolytic cell to condition the device to the conductive posture. The preplating circuit portion includes a rectifier 129 connected to the first power line 100 through door switch 104'which permits negative charging of a capacitor through the momentary start switch 106 made to the normally open contact 131. Upon the release of the momentary switch 106 for operation to its normally closed contact 133, the accumulated negative charge on capacitor 130 is discharged through resistor 134 and through the electrolytic cell 125'and chassis to ground. It is noted that the capacitor 130 is negatively charged with an accumulation of electrons on the right-hand plate 136 of the capacitor 130 so that the flow of electrons is through the electrolytic cell 125 from the gold electrode 126 to the silver electrode 127. This flow of electrons from the gold electrode 126 to the silver electrode 127 corresponds by common-practice, to the flow of current from the silver electrode to the gold electrode so that silver ions are deposited on the gold electrode 126 as previously explained, to operate the electrolytic cell 125 to the conductive posture.

It is also noted at this time that the silver electrode 127 of the electrolytic cell 125 is connected to earth ground through the conductive chassis 135 of the apparatus. In the specific embodiment of FIG. 2, the chassis 135 is maintained disconnected from or electrically isolated from the neutral line 103 within the control circuit as shown in FIG. 2. The chassis, however, becomes effectively connected to the earth-grounded neutral line of the power supply system by an external ground path. Such a circuit provision requires that the apparatus chassis be connected to the earth ground for operability of the circuit and apparatus as will be shown further herein.

The control circuit also includes a plating circuit portion extending from conductor 138 and comprising rectifier 137, resistor 139 and the pair of conductive electrodes 80 and 81 connected in series with junction 140. As wet fabrics contact and bridge the electrodes 80,81, the resistance between the electrodes will be relatively low and thus current flow therethrough will be at a high level. This current flow through the fabrics effects further plating of the electrolytic cell 125 but at a. decreasing rate as the fabrics become dry and thus of higher resistance. The rectifier 137 limits the plating to half cycle operation and the variable resistance of the fabrics across the electrodes 80,81 as a measure of the moisture content of the fabricsprovides a variable plating signal to the electrolytic cell 125.

The preplating circuit including capacitor 130 and the plating circuit including the electrodes 80,81 may thus be considered as accumulating circuit means operable for effecting a plating of the electrolytic cell 125.

A dissipating circuit is connected between the conductor 138 and the electrolytic cell 125 to effectively provide a deplating of the electrolytic cell 125 at a predetermined constant rate while the device remains in the conductive posture. The deplating path includes rectifier 141, resistor 143,.resistor 144, and rectifier 145. It is noted that the-relative positioning of rectifiers 129 and 137 relative to 141 provides that electrons flowing through the electrolytic cell 125 from the conductor 100 to the chassis 135 effect plating of the electrolytic cell 125 whereas electrons flowing from ground and through the chassis 135, the electrolytic cell 125, and the deplating circuit including rectifiers 145 and 141', effect a deplating of the electrolytic cell 125. Resistance 146 functionswith resistance 143 as a voltage divider for effecting the current flow required for the shutdown device as will be shown.

Alsoincluded in the circuit of FIG. 2 is an output circuit portion including a transistor 149 having a base 150, a collector 151, and an emitter 152. The baseemitter junction 150, 152 is responsive to the voltage drop across the electrolytic cell 125 as will be shown.-

The output circuit further includes a siliconcontrolled rectifier, or SCR 154, in circuit with the transistor 149. A capacitor 155 and resistor 156 are connected to the conductor 138. through the rectifier 141 and function as an auxiliary power supply for gating the SCR 154 to aconductive condition. The SCR 154 includes a path from the anode 157 to cathode 158 connected in series to the relay coil 107 and triggered to the conductive condition by the auxiliary power supply at'gate 159 for maintaining the relay coil 107 energized while the drying operation proceeds. A diode 163 is shown in parallel connection to the relay coil 107 for conducting the self-induced current that is produced by the collapsing magnetic field of the inductive relay coil 107 during the half cycle of normal deenergization. A snubber circuit including seriesconnected resistor 164 and capacitor 165 is in parallel connection to the SCR anode-cathode path to protect the SCR 154 against electrical transients.

The operation of the circuit of FIG. 2 for controlling operation of the dryer apparatus will now be described. With the door switch 104 in its closed position as by the closing of the door 24, manual operation of the pushto-start button 22 will close momentary switches 105 and 106 for energizing the drive motor 64 and effectively energizing the control circuit to initiate operation of the apparatus. Initially, the circuit for energizing the motor 64 extends from the first opwer line 100, through door switch 104, conductor 167, switch 105, and conductor 169 to the centrifugal switch 113. The circuit continues through the run and start windings 115 and 116 connected in parallel and through a conductor 170 to the neutral line 103.

At the same time a circuit will be completed to the relay coil 107 and extending from the first power line 100, through door switch 104, conductor 167, the momentary switch 105, and conductor 138 to one side of the coil 107. A circuit is also completed from the conductor 138 through diode 141 and conductor 171 to one side of the capacitor 155 for positive charging thereof. The capacitor 155 with resistor 156 effectively provides a positive power supply for triggering the SCR 157 to the conductive position. Thiseffects energization of the relay coil 107 by a circuit extending from conductor 138 and through the anode-cathode path of the SCR 157 and conductor 172 to the neutral line 103. Energization of the relay coil 107 closes relay switches 108 and 109.

Upon the motor 64 reaching a predetermined speed, the centrifugal switch 113 operates from the normally closed contact 114 to the normally open contact 117 for deenergizing the start winding 116 and maintaining the run winding 115 energized by a circuit which extends from the first power line 100 through the closed door switch 104 and relay switch 109 and conductor 119 to the normally open contact 117 of the centrifugal switch 113. The closing of the relay switch 108 also energizes the heater 102 by a circuit that extends from the first power line 100 through the relay switch 108, the high limit thermostat 112, the cycling thermostat 110, the heater 102, and the centrifugal switch 111 to the second power line 101.

For charging capacitor 130, closing of the momentary switch 133 to its normally open contact 131 completes a circuit between the first power line 100 and the neutral line 103. Capacitor 130 is negatively charged by the circuit that extends from the conductor 167 through rectifier 129 and through the momentary switch 106 closed to its normally open contact 131 to the negative plate 136 of the capacitor 130. The positive plate 174 of the capacitor 130 is connected to the neutral line 103 through conductor 175.

At this momentary stage of energization, the apparatus is operating with the motor 64 energized for tumbling fabrics in chamber 60 and the heater 102 energized to provide heat for drying the fabrics in the apparatus.

Upon manual release of the push-to-start button 22,.

tor 130 flow through the electrolytic cell 125 to ground. This flow of electrons corresponds to the flow of current through the electrolytic cell 125 for causing a plating action to occur within the electrolytic cell and the cell 125 becomes conductive to provide a very low impedance path to ground. The charge provided by capacitor 130 provides a one-shot predetermined plating of the electrolytic cell 125 to condition it to the conductive posture and establish a minimum period of conductive operation thereof.

With the motor 64 operating, the wet fabrics within the chamber 60 are tumbling therein for random engagement with the electrodes 80,81. The bridging of wet fabrics between the pair of electrodes 80 and 81 completes the plating circuit between the conductor 138 and the neutral line 103 for flow of electrons, as controlled by rectifier 137, through the electrolytic cell 125 to effect a further plating thereof. The circuit extends from the conductor 138 through rectifier 137, resistor 139, the electrodes 80,81 as bridged by the wet fabrics, and through the junction 140, the electrolytic cell 125, and the chassis grounding path 135 to the earth ground potential. This current flow continues during each negative half cycle at a rate depending upon the moisture content of the fabrics and will thus decrease in rate as the fabrics become more dry. The rate of plating is directly proportional to the current fiow through the electrolytic cell 125 from the silver electrode 127 to the gold electrode 126 and will thus also decrease as the fabrics become dry.

The voltage divider formed by resistances 143 and 146 establishes a resistance network to effect a predetermined current flow through the electrolytic cell 125 for deplating the electrolytic cell 125 at a generally constant rate. The deplating current flow extends through the conductive chassis grounding path 135 and the electrolytic cell 125 to the junction 140. The deplating circuit then extends from the junction 140 through rectifier 145, resistor 144, resistor 143, and rectifier 141 to the conductor 138. The rate of deplating effected by the current flow is substantially constant as determined by the impedance in the deplating path.

The relative rates of charging or plating of the electrolytic cell 125 through the electrodes 80,81 and bridging fabrics as compared to the deplating of the electrolytic cell 125 through the dissipating or deplating circuit are thus dependent upon the fabrics attaining a predetermined dryness. It is noted that while the fabrics are relatively wet at the initial portion of the cycle the rate of plating of the electrolytic cell 125 by a circuit extending through the electrodes 80,81 and wet fabrics exceeds the deplating rate through the dissipating circuit. As the dryness of the fabrics approach a preselected desired dryness, the constant rate of deplating exceeds the plating achieved through the electrodes 80,81 and fabrics so that the remaining quantity of plated material on the gold electrode 126 decreases. Eventually the electrolytic cell 125 becomes deplated, assumes a nonconductive posture, and exhibits a high voltage drop thereacross. This plating and deplating operation of the electrolytic cell 125 provides direct integration of the current flow through the electrodes 80,81 as dependent upon the moisture content of the fabrics and in addition provides the time delay period deemed necessary for proper drying.

It is desirable to provide to the operator a selection of drying cycles or of degrees of dryness. To achieve this selectivity, the built-in time delay may be made variable as by providing a variable component for capacitor 130. Alternatively, one or more of the resistors 139, 143, 144 and 146 could be made variable. For convenience of explanation in this specification, however, the components are considered fixed.

When the electrolytic cell 125 is plated, the voltage at the junction 177 is essentially the voltage drop across rectifier 145 since the electrolytic cell 125 has a conductive posture. This same voltage is impressed across rectifier 179 and the base-emitter junction 150,152 of transistor 149. This voltage level, however, at the baseemitter junction 150,152 of transistor 149 is insuffcient to cause transistor 149 to conduct across the collector-emitter junction 151,152. As the clothes become dry, however, the electrolytic cell 125 becomes deplated and changes to a relatively high impedance posture as previously shown. The electrolytic cell 125 thus becomes nonconductive in comparison to the path through rectifier 179 and base-emitter junction 150,152 of transistor 149. Further, the increased voltage drop across the series circuit extending from junction 177 and including electrolytic cell 125, conductive chassis 135, and ground connector 87 is impressed on the base-emitter junction 150,152 of transistor 149 and with the resulting increased current flow through the base-emitter junction 150,152 causing the transistor 149 to become significantly more conductive across the collector-emitter junction 151,152. The current path to the base-emitter junction 150,152 extends from conductor 138, through rectifier 141, resistor 143, resistor 144, and rectifier 179 to the transistor base 150.

The conductive path through the transistor 149 shunts the SCR gate signal which is provided to the SCR 154 through resistor 156. The SCR 154 then ceases conduction to deenergize the relay coil 107 and thereby open relay switches 108 and 109. Opening of switch 108 deenergizes the heater circuit while opening of switch 109 deenergizes the motor circuit unless the cool-down thermostat has been operated to the closed position. If the cool-down thermostat 120 has closed, the motor 64 will remain energized until the thermostat reset temperature is reached. During this time, the motor 64 remains energized by a circuit extending between the first power line 100 through the door switch 104, the conductor 180, the cool-down thermostat 120, conductor 119, and the centrifugal switch 113 made to the normally open contact 117.

During the cool-down period, a circuit will also be completed from the first power line 100 through the cool-down thermostat 120, conductor 119, the centrifugal switch 113 made to the normally open contact 117, through conductor 169 and conductor 138 to one side of rectifier 141. A power supply thus remains to the capacitor and permits current flow through resistor 143, resistor 144, rectifier 179 and the baseemitter junction 150,152 of transistor 149 to maintain the transistor 149 conductive and the SCR 154 nonconductive so that the relay coil 107 remains deenergized during the cool-down operation.

Upon the temperature decreasing to the established temperature for opening the cool-down thermostat 120, the motor 64 will be deenergized and the control 1 1 circuit deenergized for effectively terminating operation of the apparatus.

Note also in FIG. 2' that rectifiers 145 and. 179 are placed'in a back-to-back relationship toprevent damage to the circuit components in case a two-wire connector is utilized, such as in a 120-volt gas appliance, where the user could inadvertently interchange the neutral and hot power lines at the appliance input connections. In the circuit of FIG. 2, the neutral line 103 is connected to the emitter terminal 152 of the transistor 149 and a ground'line is connected to the electrolytic cell 125. Should .a two-wire connection be used and should the plug be reversed, the line to the emitter 152 of transistor 149 would become the hot line and there would be IZO-volt differential between the emitt'er of transistor 149. and ground. This differential could cause damaging current to flow both through the transistor' 149 and the electrolytic cell 125 .were it not blocked by the back-to-back relationship of rectifiers 145 and'179.

.The circuit for preplating the electrolytic cell 125 is provided to insure proper operation of the device and in particular 'toprovide the ability to dry'small loads. This preplating provides a guaranteed heat time so that regardless of the amount of plating or deplating the time delay provides a minimum drying operation.

is effected by depressing the manually operable pushto-start switch 22 which closes switch 105 to energize relay 107 for in turn energizing the motor 64 and heater 102. It has been noted also that operation of the apparatus is terminated upon the electrolytic cell 125 becoming deplated and effectively nonconductive so that the increased voltage drop and resulting increased current flow to the base-emitter junction 150,152 effects a significantly higher level of conduction across the coilector-emitter junction 151,152 for shunting the SCR 154 toanonconductive condition. The SCR in the nonconductive condition deenergizes or prevents energization of the relay.

It is also noted that the absence of a conductor 87 be- I tween the chassis 135 and earth ground, as when the apparatus-is not grounded, produces a high voltage drop in the series circuit that extends from junction 177 to earth ground. The transistor 149 responds to the high voltage drop and becomes conductive to shunt SCR 154 and prevent energization of relay 107. Though the motor 64 is momentarily energized while the button 22 is depressed, operation of the apparatus is effectively precluded since all operation will cease when button 22 is released. The inoperability of the apparatus indicates to the operator that the machine is not grounded or at least indicates that service is'required before the machine may be used. The terminology operation is precluded. is intended to include interrupting operation, preventing operation, and initiating termination of operation.

In order for the circuit of FIG. 2 to be operable in a manner tov preclude operation of the apparatus in the absence of the earth ground it is essential that the conductor 87 be disconnected, within the control circuit, from the conductor 103, and that chassis 135 be disconnected, within the control circuit, from conductor 103.

In a normal household electrical service installation the conductors 100,101, and 103 are connected through a plug and receptacle arrangement to the incoming service. The electrical service includes a stepdown transformer having a secondary winding of which the neutral side is connected to earth ground, as by a ground wire at the power pole. Therefore, when the apparatus is connected to earth ground, a circuit is effectively completed from chassis 135 through conductor 87, through an earth-ground path external to the circuit, and to the neutral conductor through the ground connection in theelectrical distribution system. Further details and explanation of operation of a similar control circuit utilizing the external ground path as an essential portion of the enabling circuit is included in copending application Ser. No. 405,203 filed Oct. 10, 1973, by the instant inventor and assigned to the assignee of the instant application.

In a still further alternateembodirnent of a circuit for requiring an earth ground connection for operabilityof the apparatus, a ground sensitive control could be provided that would eliminate the dryness sensing portion of FIG. 2 and also eliminates the electrolytic cell. In the absence of the electrolytic cell, a series circuit portion including the earth ground connector would be connected to a transistor in a manner similar to that shown in FIG. 2. The absence of a ground connection in the circuit leg parallel to the base-emitter junction of the transistor would provide a high voltage signal to the transistor for conductive operation thereof to prevent energization of the relay and thus prevent operabilit of the apparatus.

For the purposes of a particular reduction to practice of the circuit of FIG. 2 the following values of components were utilized:

it is clear that the circuit described hereinabove achieves a novel combination of components comprising a fabric dryness sensing circuit for controlling operation of a drying apparatus while also possessing ground sensitive characteristics for requiring the presence of an earth ground connection for operability of the apparatus. These accomplishments permit an improved circuit having more compact features and which may potentially be providedat a lower cost.

In the drawings and specification there has been set forth a preferred embodiment of the invention and although specific terms are employed these are used in a generic and descriptive sense only and not for purposes of limitation. Changes in form and the proportion of parts as well as the substitution of equivalents are contemplated as circumstances may suggest or render expedient without departing from the spirit or scope of the invention as further defined in the following claims.

I claim:

1. A control for an apparatus and including a control circuit connectable to an electrical supply where one wire of said electrical supply is a power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; a series circuit portion disposed electrically between said first and second conductors and including a first terminal effectively electrically connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit; chassis grounding means connected to said second terminal to provide a relatively low resistance chassis path from said second terminal to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit between said first and second conductors through said series circuit portion includes said chassis path and an earth ground path external to said control circuit; electrical means in said series circuit portion operable in the absence of completion of said electrical circuit for producing a predetermined electrical condition; and output circuit means effectively connected between said first and second conductors and responsive to said predetermined electrical condition for precluding operation of said apparatus whereby operability of said apparatus is dependent on the presence of an earth grounding of said apparatus.

2. A control as defined in claim 1 and further including means for initiating operation of said apparatus and said control circuit including means for providing a momentary power supply to said first terminal and wherein the presence of said power supply and the absence of completion of said electrical circuit'produces a predetermined voltage condition in said series circuit portion.

3. A control as defined in claim 1 wherein said electrical means includes an integrating switch operable from a nonconductive condition to a conductive condition upon energization of said apparatus in the presence of completion of said electrical circuitincluding said earth ground path for effectively preventing production of said predetermined electrical condition.

4. A control for an apparatus including a control circuit connectable to an electrical supply where one wire of said electrical supply is a power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; a series circuit portion including a first terminal effectively electrically connected to'said first conductor and a second terminal effectively electrically disconnected from said second conductor within said' control circuit; chassis grounding means connected to said second terminal and to earth ground to provide a relatively low resistance chassis path from said second terminal to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit between said first and second conductors through said series circuit portion includes the chassis path and an earth ground path external to said control circuit; and output circuit means effectively connected between said first and second conductors and including semiconductor amplifier means effectively connected to said series circuit portion and responsive to the absence of completion of said electrical circuit through said chassis path and said earth ground path for precluding operation of said apparatus whereby operability of said apparatus is dependent on the presence of an earth grounding of said apparatus.

5. In a control as defined in claim 4 wherein a predetermined voltage condition is produced in said series circuit responsive to the absence of completion of said electrical circuit and wherein said amplifier means includes a transistor having a base connected to said series circuit portion and responsive to said high voltage condition.

6. In a control as defined in claim 4 wherein said series circuit portion includes an electrolytic cell responsive to completion of said electrical circuit and conduction of current through said electrolytic cell for operation to a conductive condition for preventing production of said predetermined electrical condition.

7. In a control as defined in claim 6 and further comprising a manually operable momentary switch for providing a momentary supply of current to said electrolytic cell to effect operation thereof to said conductive condition in the presence of completion of said electri cal circuit.

8. A control for an apparatus and including a control circuit connectable to an electrical supply where one wire of said electrical supply is a power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; a circuit portion disposed electrically between said first and second conductors and including a first terminal electrically connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit and connected to a relatively low resistance chassis path to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit between said first and second'com ductors through said circuit portion includes the chassis path and an earth ground path external to said control circuit; means for initiating operation of said appa ratus and said control circuit including means for providing a momentary power supply to said circuit portion; electrical means associated with said circuit portion and operable in the absence of completion of said electrical circuit through said chassis path and said earth ground path and in the presence of said momentary power supply for producing a predetermined electrical condition; and output circuit means effectively connected between said first and second conductors and responsive to said predetermined electrical condition for precluding operation of said apparatus.

9. A control as defined in claim 8 wherein said circuit portion includes a series circuit having an electroytic cell disposed between said first and second terminals and responsive to said momentary power supply in the presence of completion of said electrical circuit through said earth ground path for operation to said conductive condition toprevent production of said pre determined electrical condition.

10. A control for an apparatus and including a control circuit connectable to an electrical supply where one wire of said electrical supply is the power line and another wire is an earth-grounded neutral line; the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; first circuit means connected to said first conductor and operable for initiating energization of said apparatus and said control circuit; second circuit means effectively connected between said first and second conductors and operable for control ling continued energization of said apparatus and including a series circuit portion having a first terminal effectively connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit; chassis grounding means for connecting said second terminal through a relatively low resistance chassis path to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit through said series circuit portion includes said chassis path and an earth ground path external to said control circuit, said first circuit means including means for providing a momentary power supply to said first terminal,. said series circuit portion being operable in the absence of completion of said electrical circuit and in the presence of said momentary power supply for producing a predetermined electrical condition; and output means effectively connected between said first and second conductors and responsive to said predetermined electrical condition for precluding operation of said apparatus whereby operability of said apparatus is dependent on the presence of an earth grounding of said apparatus.

11. A control as defined in claim 10 wherein electrical means associated with said second circuit means includes a normally nonconductive electrolytic device operative in the absence of completion of said electrical circuit for producing a predetermined voltage across said electrolytic cell and wherein further said output circuit means is responsive to said predetermined voltage for precluding operation of said apparatus whereby an earth grounding of said apparatus is essential to operability of said apparatus.

12. A control for an apparatus as defined in claim 10 wherein said circuit portion includes an electrolytic device and wherein said second circuit means includes an accumulating circuit portion and a dissipating circuit portion for effecting a charging and discharging of said electrolytic cell and wherein further the absence of completion of said electrolytic circuit through said electrolytic cell maintains said electrolytic cell in a nonconductive condition for producing said predetermined electrical condition in the form of a predetermined voltage signal.

13. A control for an apparatus and including a control circuit connectable to an electrical supply where on wire of said electrical supply is a power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; first circuit means connected between said first and second conductors and operable for initiating energization of said apparatus and said control circuit; second circuit means connected between said first and second conductors and operable for controlling continued energization of said apparatus and including a circuit portion comprising an electrolytic device, said electrolytic device having a first terminal effectively connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit; chassis grounding means for connecting said second terminal through a relatively low resistance chassis path to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit through said electrolytic device includes said chassis path and an earth ground pathexternal to said control circuit, said electrolytic device being normally nonconductive and responsive to current flow therethrough for operation to a conductive condition and responsive to the absence of current flow therethrough for effecting a predetermined voltage condition; and output circuit means effectively connected between said first and second conductors responsive to said predetermined voltage condition for precluding operation of said apparatus.

14. A control for an apparatus as defined in claim 13 wherein said first circuit means includes a manually operable momentary switch operable while depressed for effecting energization of the machine and competing a momentary power supply to said electrolytic device,

' said electrolytic device in the absence of an earth grounding of said apparatus being operable for assuming said predetermined voltage condition to terminate operation of said apparatus upon release of said momentary switch. 

1. A control for an apparatus and including a control circuit connectable to an electrical supply where one wire of said electrical supply is a power line and another wire is an earthgrounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; a series circuit portion disposed electrically between said first and second conductors and including a first terminal effectively electrically connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit; chassis grounding means connected to said second terminal to provide a relatively low resistance chassis path from said second terminal to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit between said first and second conductors through said series circuit portion includes said chassis path and an earth ground path external to said control circuit; electrical means in said series circuit portion operable in the absence of completion of said electrical circuit for producing a predetermined electrical condition; and output circuit means effectively connected between said first and second conductors and responsive to said predetermined electrical condition for precluding operation of said apparatus whereby operability of said apparatus is dependent on the presence of an earth grounding of said apparatus.
 2. A control as defined in claim 1 and further including means for initiating operation of said apparatus and said control circuit including means for providing a momentary power supply to said first terminal and wherein the presence of said power supply and the absence of completion of said electrical circuit produces a predetermined voltage condition in said series circuit portion.
 3. A control as defined in claim 1 wherein said electrical means includes an integrating switch operable from a nonconductive condition to a conductive condition upon energization of said apparatus in the presence of completion of said electrical circuit including said earth ground path for effectively preventing production of said predetermined electrical condition.
 4. A control for an apparatus including a control circuit connectable to an electrical supply where one wire of said electrical supply is a power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; a series circuit portion including a first terminal effectively electrically connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit; chassis grounding means connected to said second terminal and to earth ground to provide a relatively low resistance chassis path from said second terminal to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit between said first and second conductors through said series circuit portion includes the chassis path and an earth ground path external to said control circuit; and output circuit means effectively connected between said first and second conductors and including semiconductor amplifier means effectively connected to said series circuit portion and responsive to the absence of completion of said electrical circuit through said chassis path and said earth ground path for precluding operation of said apparatus whereby operability of said apparatus is dependent on the presence of an earth grounding of said apparatus.
 5. In a control as defined in claim 4 wherein a predetermined voltage condition is produced in said series circuit responsive to the absence of completion of said electrical circuit and wherein said amplifier means includes a transistor having a base connected to said series circuit portion and responsive to said high voltage condition.
 6. In a control as defined in claim 4 wherein said series circuit portion includes an electrolytic cell responsive to completion of said electrical circuit and conduction of current through said electrolytic cell for operation to a conductive condition for preventing production of said predetermined electrical condition.
 7. In a control as defined in claim 6 and further comprising a manually operable momentary switch for providing a momentary supply of current to said electrolytic cell to effect operation thereof to said conductive condition in the presence of completion of said electrical circuit.
 8. A control for an apparatus and including a control circuit connectable to an electrical supply where one wire of said electrical supply is a power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; a circuit portion disposed electrically between said first and second conductors and including a first terminal electrically connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit and connected to a relatively low resistance chassis path to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit between said first and second conductors through said circuit portion includes the chassis path and an earth ground path external to said control circuit; means for initiating operation of said apparatus and said control cirCuit including means for providing a momentary power supply to said circuit portion; electrical means associated with said circuit portion and operable in the absence of completion of said electrical circuit through said chassis path and said earth ground path and in the presence of said momentary power supply for producing a predetermined electrical condition; and output circuit means effectively connected between said first and second conductors and responsive to said predetermined electrical condition for precluding operation of said apparatus.
 9. A control as defined in claim 8 wherein said circuit portion includes a series circuit having an electroytic cell disposed between said first and second terminals and responsive to said momentary power supply in the presence of completion of said electrical circuit through said earth ground path for operation to said conductive condition to prevent production of said predetermined electrical condition.
 10. A control for an apparatus and including a control circuit connectable to an electrical supply where one wire of said electrical supply is the power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; first circuit means connected to said first conductor and operable for initiating energization of said apparatus and said control circuit; second circuit means effectively connected between said first and second conductors and operable for controlling continued energization of said apparatus and including a series circuit portion having a first terminal effectively connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit; chassis grounding means for connecting said second terminal through a relatively low resistance chassis path to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit through said series circuit portion includes said chassis path and an earth ground path external to said control circuit, said first circuit means including means for providing a momentary power supply to said first terminal, said series circuit portion being operable in the absence of completion of said electrical circuit and in the presence of said momentary power supply for producing a predetermined electrical condition; and output means effectively connected between said first and second conductors and responsive to said predetermined electrical condition for precluding operation of said apparatus whereby operability of said apparatus is dependent on the presence of an earth grounding of said apparatus.
 11. A control as defined in claim 10 wherein electrical means associated with said second circuit means includes a normally nonconductive electrolytic device operative in the absence of completion of said electrical circuit for producing a predetermined voltage across said electrolytic cell and wherein further said output circuit means is responsive to said predetermined voltage for precluding operation of said apparatus whereby an earth grounding of said apparatus is essential to operability of said apparatus.
 12. A control for an apparatus as defined in claim 10 wherein said circuit portion includes an electrolytic device and wherein said second circuit means includes an accumulating circuit portion and a dissipating circuit portion for effecting a charging and discharging of said electrolytic cell and wherein further the absence of completion of said electrolytic circuit through said electrolytic cell maintains said electrolytic cell in a nonconductive condition for producing said predetermined electrical condition in the form of a predetermined voltage signal.
 13. A control for an apparatus and including a control circuit connectable to an electrical supply where on wire of said electrical supply iS a power line and another wire is an earth-grounded neutral line, the combination comprising: means for connecting said control circuit to said electrical supply including first and second conductors; first circuit means connected between said first and second conductors and operable for initiating energization of said apparatus and said control circuit; second circuit means connected between said first and second conductors and operable for controlling continued energization of said apparatus and including a circuit portion comprising an electrolytic device, said electrolytic device having a first terminal effectively connected to said first conductor and a second terminal effectively electrically disconnected from said second conductor within said control circuit; chassis grounding means for connecting said second terminal through a relatively low resistance chassis path to earth ground, said second conductor being disconnected within said control circuit from said low resistance chassis path whereby completion of an electrical circuit through said electrolytic device includes said chassis path and an earth ground path external to said control circuit, said electrolytic device being normally nonconductive and responsive to current flow therethrough for operation to a conductive condition and responsive to the absence of current flow therethrough for effecting a predetermined voltage condition; and output circuit means effectively connected between said first and second conductors responsive to said predetermined voltage condition for precluding operation of said apparatus.
 14. A control for an apparatus as defined in claim 13 wherein said first circuit means includes a manually operable momentary switch operable while depressed for effecting energization of the machine and competing a momentary power supply to said electrolytic device, said electrolytic device in the absence of an earth grounding of said apparatus being operable for assuming said predetermined voltage condition to terminate operation of said apparatus upon release of said momentary switch. 